The emerging field of tissue engineering (TE) is poised to make enormous progress in the treatment of organ disease and dysfunction in the coming decade. In 2001, there were 23 cell-based therapeutics approved for market in the United States (U.S.) and Europe, of which nine were skin substitutes or grafts, and 100 more products were in development. (De Bree, Genomics-based Drug Data Report and Regenerative Therapy (1) 2:77-96 (2001)). A decade later, engineered tissues have emerged as a discrete industry sector within the wound care industry and represent one of regenerative medicine's most promising cell based therapeutic platforms. The global wound care market was estimated to be $16.8 billion in 2012 and has been growing at a rate of approximately 6% annually (Kalorama Information, April 2012). The bulk of this market is comprised of traditional sectors that are mature and highly competitive, and include products targeting basic and advanced wound care, wound closure, and anti-infectives. This has led competitors to increasingly focus their attention on developing highly differentiated products in the more innovative active wound care sector, a sector that represents approximately 15% of the overall market. While sales of negative pressure wound therapy still predominate, 2010 sales of engineered tissues and other products within the U.S. biologics market grew to $448 million, and are projected to increase to $1.058 billion by 2015, a compound annual growth rate of 18.8% (BioMedGPS-SmarTRAK market analysis, 2012).
Although a multitude of revolutionary and economically important applications for engineered tissues and organs exist in the human health arena, the full economic potential of the industry is far from realized. At present, only two tissue engineering companies worldwide have been able to commercialize cell based, skin substitute products focused on cutaneous wound healing and achieve annual sales in excess of $100 million.
A major impediment to the acceptance of engineered tissues by medical practitioners, healthcare providers, and second party payers is the lack of a means to effectively and efficiently preserve and store engineered tissues. The nature of living cells and tissue products makes development of long-term storage challenging. Current engineered tissues must often be stored and shipped under carefully controlled conditions to maintain viability and function. Typically, engineered tissue products take weeks or months to produce but must be used within hours or days after manufacture. As a result, TE companies must continually operate with their production facilities at top capacity and absorb the costs of unsold product which must be discarded. These inventory losses, on top of already costly manufacturing process, have forced prices to impractical levels. As one specific example, APLIGRAF requires about four weeks to manufacture, is usable for only 15 days and must be maintained between 20 and 23° C. until used. As another example, EPICEL is transported by a nurse from Genzyme Biosurgery's production facility in Cambridge, Mass. to the point of use in a portable incubator and is used immediately upon arrival. Such constraints represent significant challenges to developing convenient and cost-effective products.
Cryopreservation has been explored as a solution to the storage problem, but it is known to induce tissue damage through ice formation, chilling injury, and osmotic imbalance. Besides APLIGRAF, the only other approved living skin equivalent, ORCEL, has been evaluated as a frozen product but had the drawback that it must be maintained at temperatures below −100° C. prior to use. This requires specialized product delivery and storage conditions, including the use of dangerous goods during transport, and use of liquid nitrogen for storage, which is expensive, dangerous, and not readily available in rural clinics and field hospitals.
Accordingly, what is needed in the art are improved methods of cryopreserving viable engineered tissues and cells for storage under conditions that are routinely available at the point of use.